[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel][PATCH]ioemu:fix up error when using qemu-img-xen to create img



On Tue, May 05, 2009 at 03:17:34PM +0100, Ian Jackson wrote:
> 
> Consider a raw disk image file which is writeable by a guest.  (This
> is of course one very common usage model.)  The guest can write
> anything it likes to the image file, including anything to the start
> of the file - where the cow header would be if it were a cow file.
> 
> So it can, if it likes, write a cow header (qcow2 for example) to the
> start of its `virtual disk image'.  Qemu's cow headers contain the
> pathname of the backing file, and the guest can of course name any
> file it likes.
> 
> If this image, which is supposedly a raw image, is then opened by any
> tool which autoguesses the format, that tool will then spot the cow
> header written by the guest and access the backing file (in the
> context of the host) specified by the guest.
> 
> Depending on the exact circumstances this can allow the guest to get
> copies of or even complete read access to any data of its choice in
> the host.
> 
> Upstream qemu have fixed this problem in a half-hearted way and
> evidently their qemu-img is still vulnerable.  We have changed the
> format-determination code in block.c so that any attempt to autodetect
> a format never returns `raw'; that means that any vulnerable code
> anywhere is instantly fixed although it may break some existing usages
> in cases where we haven't properly plumbed through a specification of
> the image format.

Wasn't the upstream change to add a '-F baseimage_format' enough to
allow the flaw to be avoided when creating new images ? Or are you
attempting to prevent the issue, even when -F is not used ?

Daniel
-- 
|: Red Hat, Engineering, London   -o-   http://people.redhat.com/berrange/ :|
|: http://libvirt.org  -o-  http://virt-manager.org  -o-  http://ovirt.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: GnuPG: 7D3B9505  -o-  F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.